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Träfflista för sökning "WFRF:(Johansson Kenneth) ;conttype:(refereed)"

Sökning: WFRF:(Johansson Kenneth) > Refereegranskat

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31.
  • Broitman, E., et al. (författare)
  • Electrical and optical properties of CNx(0=x=0.25) films deposited by reactive magnetron sputtering
  • 2001
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:2, s. 1184-1190
  • Tidskriftsartikel (refereegranskat)abstract
    • The electrical and optical properties of carbon-nitride CNx films (O=x=0.25) deposited by unbalanced reactive magnetron sputtering from a graphite target in mixed Ar/N2 discharges at a substrate temperature of 350°C have been investigated. Pure C films exhibit a dark conductivity at room temperature of 250 O-1 cm-1, which grows up to 250 O-1 cm-1 for CNx films with N content of 20%. For CNx films, temperature-dependent conductivity measurements suggest that two electron conduction processes exist in the investigated temperature range 130
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32.
  • Brändén, Gisela, 1975, et al. (författare)
  • Coherent diffractive imaging of microtubules using an X-ray laser.
  • 2019
  • Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray free electron lasers (XFELs) create new possibilities for structural studies of biological objects that extend beyond what is possible with synchrotron radiation. Serial femtosecond crystallography has allowed high-resolution structures to be determined from micro-meter sized crystals, whereas single particle coherent X-ray imaging requires development to extend the resolution beyond a few tens of nanometers. Here we describe an intermediate approach: the XFEL imaging of biological assemblies with helical symmetry. We collected X-ray scattering images from samples of microtubules injected across an XFEL beam using a liquid microjet, sorted these images into class averages, merged these data into a diffraction pattern extending to 2 nm resolution, and reconstructed these data into a projection image of the microtubule. Details such as the 4 nm tubulin monomer became visible in this reconstruction. These results illustrate the potential of single-molecule X-ray imaging of biological assembles with helical symmetry at room temperature.
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33.
  • Chinga-Carrasco, Gary, et al. (författare)
  • Structural effects on print-through and set-off
  • 2012
  • Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:3, s. 596-603
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study the effect of paper structure on ink transfer and cold-set print quality was assessed. A factorial experiment involving 5 factors with two levels was designed. Several sheet structures were constructed. The sheets were made from three basic pulps, thermomechanical pulp (TMP), de-inked pulp (DIP) and stone groundwood (SGW). The designed structures were homogeneous and layered to verify the effect of sheet structure and fines content on print quality. A comprehensive multiscale characterisation of the sheet structures was performed. The analyses comprised scanning electron microscopy (SEM) and mercury porosimetry for bulk structure assessment. Parker Print Surf (PPS), laser profilometry and field-emission scanning electron microscopy (FE-SEM) were applied for giving a detailed description of the surface structure affecting ink transfer. The study revealed that the surface structure affects the ink demand and set-off. Increasing the micro-roughness leads to an increment of ink demand in order to achieve a given print density. The bulk pore structure affects the light scattering coefficients. Small pores are positive for increasing the light scattering and thus for reducing the print-through level. This was confirmed by SEM and mercury porosimetry measurements.
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34.
  • Collins, Ruairi, et al. (författare)
  • Biochemical discrimination between selenium and sulfur 1 : a single residue provides selenium specificity to human selenocysteine lyase
  • 2012
  • Ingår i: PLoS One. - Stockholm : Karolinska Institutet, Dept of Medical Biochemistry and Biophysics. - 1932-6203.
  • Tidskriftsartikel (refereegranskat)abstract
    • Selenium and sulfur are two closely related basic elements utilized in nature for a vast array of biochemical reactions. While toxic at higher concentrations, selenium is an essential trace element incorporated into selenoproteins as selenocysteine (Sec), the selenium analogue of cysteine (Cys). Sec lyases (SCLs) and Cys desulfurases (CDs) catalyze the removal of selenium or sulfur from Sec or Cys and generally act on both substrates. In contrast, human SCL (hSCL) is specific for Sec although the only difference between Sec and Cys is the identity of a single atom. The chemical basis of this selenium-over-sulfur discrimination is not understood. Here we describe the X-ray crystal structure of hSCL and identify Asp146 as the key residue that provides the Sec specificity. A D146K variant resulted in loss of Sec specificity and appearance of CD activity. A dynamic active site segment also provides the structural prerequisites for direct product delivery of selenide produced by Sec cleavage, thus avoiding release of reactive selenide species into the cell. We thus here define a molecular determinant for enzymatic specificity discrimination between a single selenium versus sulfur atom, elements with very similar chemical properties. Our findings thus provide molecular insights into a key level of control in human selenium and selenoprotein turnover and metabolism.
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35.
  • Deckner, Fanny, et al. (författare)
  • Sheet pile behavior during vibratory driving : numerical study based on a field test
  • 2017
  • Ingår i: Soil Dynamics and Earthquake Engineering. - 0267-7261 .- 1879-341X.
  • Tidskriftsartikel (refereegranskat)abstract
    • Vibrations due to sheet pile driving are a problem in many urban areas today. Increased knowledgeof the vibration transfer process from source to nearby objects is important in order to enableminimization of induced vibrations. The transfer of vibrations from sheet pile to soil is dependent onthe sheet pile behaviour during driving. This paper presents a 3D finite element study of thebehaviour of a vibratory driven sheet pile, complementing results from a full-scale field test. Thefinite element model accounts for strain dependent soil stiffness using an equivalent linear soilmodel. The conclusion is that the sheet pile bends considerably during driving with eccentricclamping. Furthermore, it is shown that the bending mode is similar irrespective of sheet pilepenetration depth.
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36.
  • Dewhurst, Richard, et al. (författare)
  • How task demands influence scanpath similarity in a sequential number-search task
  • 2018
  • Ingår i: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; , s. 9-23
  • Tidskriftsartikel (refereegranskat)abstract
    • More and more researchers are considering the omnibus eye movement sequence—the scanpath—in their studies of visual and cognitive processing (e.g. Hayes, Petrov, & Sederberg, 2011; Madsen, Larson, Loschky, & Rebello, 2012; Ni et al., 2011; von der Malsburg & Vasishth, 2011). However, it remains unclear how recent methods for comparing scanpaths perform in experiments producing variable scanpaths, and whether these methods supplement more traditional analyses of individual oculomotor statistics. We address this problem for MultiMatch (Jarodzka et al., 2010; Dewhurst et al., 2012), evaluating its performance with a visual search-like task in which participants must fixate a series of target numbers in a prescribed order. This task should produce predictable sequences of fixations and thus provide a testing ground for scanpath measures. Task difficulty was manipulated by making the targets more or less visible through changes in font and the presence of distractors or visual noise. These changes in task demands led to slower search and more fixations. Importantly, they also resulted in a reduction in the between-subjects scanpath similarity, demonstrating that participants’ gaze patterns became more heterogenous in terms of saccade length and angle, and fixation position. This implies a divergent strategy or random component to eye-movement behaviour which increases as the task becomes more difficult. Interestingly, the duration of fixations along aligned vectors showed the opposite pattern, becoming more similar between observers in 2 of the 3 difficulty manipulations. This provides important information for vision scientists who may wish to use scanpath metrics to quantify variations in gaze across a spectrum of perceptual and cognitive tasks. © 2018 Elsevier Ltd
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37.
  • Dewhurst, Richard, et al. (författare)
  • It depends on how you look at it: Scanpath comparison in multiple dimensions with MultiMatch, a vector-based approach
  • 2012
  • Ingår i: Behavior Research Methods. - : Springer Science and Business Media LLC. - 1554-3528.
  • Tidskriftsartikel (refereegranskat)abstract
    • Eye movement sequences---or scanpaths---vary depending on stimulus characteristics and task (Foulsham \& Underwood, 2008; Land, Mennie, \& Rusted, 1999). Common methods for comparing scanpaths, however, are limited in their ability to capture both the spatial and temporal properties of which a scanpath consists. Here we validate a new method for scanpath comparison based on geometric vectors, which compares scanpaths over multiple dimensions retaining positional and sequential information (Jarodzka, Holmqvist, \& Nyström, 2010). `MultiMatch' was tested in two experiments and pitted against ScanMatch (Cristino, Mathôt, Theeuwes, \& Gilchrist, 2010), the most comprehensive adaptation of the popular Levenshtein method. Experiment 1 used synthetic data, demonstrating the greater sensitivity of MultiMatch to variations in spatial position. In experiment 2 real eye movement recordings were taken from participants viewing sequences of dots, designed to elicit scanpath pairs with commonalities known to be problematic for algorithms (for example, when one scanpath is shifted in locus, or fixations fall either side of an AOI boundary). Results illustrate the advantages of a multidimensional approach, revealing how two scanpath differ. For instance, if one scanpath is the reverse copy of another the difference is in direction but not the position of fixations; or if a scanpath is scaled down, the difference is in the length of saccadic vectors but not overall shape. As well as having enormous potential for any task in which consistency in eye movements is important (e.g. learning), MultiMatch is particularly relevant for "eye movements to nothing" in mental imagery research and embodiment of cognition, where satisfactory scanpath comparison algorithms are lacking.
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38.
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39.
  • Dods, Robert, 1989, et al. (författare)
  • From Macrocrystals to Microcrystals: A Strategy for Membrane Protein Serial Crystallography.
  • 2017
  • Ingår i: Structure. - : Elsevier BV. - 1878-4186 .- 0969-2126. ; 25:9, s. 1461-1468
  • Tidskriftsartikel (refereegranskat)abstract
    • Serial protein crystallography was developed at X-ray free-electron lasers (XFELs) and is now also being applied at storage ring facilities. Robust strategies for the growth and optimization of microcrystals are needed to advance the field. Here we illustrate a generic strategy for recovering high-density homogeneous samples of microcrystals starting from conditions known to yield large (macro) crystals of the photosynthetic reaction center of Blastochloris viridis (RCvir). We first crushed these crystals prior to multiple rounds of microseeding. Each cycle of microseeding facilitated improvements in the RCvir serial femtosecond crystallography (SFX) structure from 3.3-Å to 2.4-Å resolution. This approach may allow known crystallization conditions for other proteins to be adapted to exploit novel scientific opportunities created by serial crystallography.
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40.
  • Dods, Robert, 1989, et al. (författare)
  • Ultrafast structural changes within a photosynthetic reaction centre.
  • 2021
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 589:7841, s. 310-314
  • Tidskriftsartikel (refereegranskat)abstract
    • Photosynthetic reaction centres harvest the energy content of sunlight by transporting electrons across an energy-transducing biological membrane. Here we use time-resolved serial femtosecond crystallography1 using an X-ray free-electron laser2 to observe light-induced structural changes in the photosynthetic reaction centre of Blastochloris viridis on a timescale of picoseconds. Structural perturbations first occur at the special pair of chlorophyll molecules of the photosynthetic reaction centre that are photo-oxidized by light. Electron transfer to the menaquinone acceptor on the opposite side of the membrane induces a movement of this cofactor together with lower amplitude protein rearrangements. These observations reveal how proteins use conformational dynamics to stabilize the charge-separation steps of electron-transfer reactions.
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